This project will investigate the neural mechanisms that mediate involuntary or reflexive attention. We will examine the behavioral and neural correlates of involuntary or reflexive attention in both visual and auditory modalities. We will use dual task methods to control carefully available attentional resources while simultaneously probing with task irrelevant stimuli. We predict that the capture of attention by particular irrelevant events will be modulated by the attentional demands of the primary task and by the properties of the irrelevant stimuli themselves. Electrophysiological, neuroimaging, and behavioral measures will be acquired to determine the relative timing of involuntary attentional shifts, the brain regions that are engaged by involuntary attention, and the behavioral consequences of involuntary attention shifts upon processing. The acquisition of event-related potentials (ERPs) and event-related functional magnetic resonance imaging (fMRI time-locked to the occurrence of task-irrelevant events) provide a covert measurement of neural activity that avoids the contamination attendant to reaction time or detection methods. The studies described herein complement those of Project 2 that examine voluntary allocation of attention to task-relevant events, and those of Project 3 that examine distraction and recent sequence upon memory maintenance. We propose three Specific Aims. In the first Aim, we will investigate the time course of reflexive attention to unpredictive peripheral visual cues by evaluating the facilitation and inhibition of visual discrimination judgments made subsequently at those peripherally cued locations. We will also investigate whether the biphasic pattern of initial facilitation and subsequent inhibition of processing typically observed at peripherally cued locations depends upon available attentional resources in the visual domain. In the second Aim, we will investigate putative automatic processes in the auditory system that are evoked by discrete physical changes or deviations in irrelevant auditory stimuli. We will examine whether these processes are limited by available intermodal and intramodal attentional resources. In the third Aim, we will investigate two stimulus properties, their alerting or signaling value and their local probability or sequence, to determine whether their ability to summon attention involuntarily is influenced by available intermodal and intramodal attentional resources.